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Thesis (MScEng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Improvements in the area of satellite orientation control in the presence of large actuator gain changes are investigated. Gain changes primarily originate from actuator failures, but may also result from intermittent sensor availability and geomagnetic field effects. The stability and performance of a classic LQR control solution under these conditions is analyzed through simulation, and two adaptive schemes are developed to improve the response. The adaptive schemes mix elements from bang-bang control to increase performance, and banded control to increase robustness. These control schemes are thoroughly tested through simulation and the results are compared with those obtained for the classic solution. Extensive modelling of the system in the MATLAB™ environment is done to support the analysis of the controllers, and hardware sensors are built to provide realistic orientation measurements to the controllers. / AFRIKAANSE OPSOMMING: Verbeterings in die veld van satelliet oriëntasie beheer in die gevalle waar die aktueerders groot veranderinge in aanwins toon, word ondersoek. Aanwins veranderinge word primêr veroorsaak deur aktueerder falings, maar kan ook deur diskontinue sensor metings en magneetveld effekte van die aarde veroorsaak word. Die stabiliteit en gehalte van 'n klassieke LQR beheer strategie onder hierdie omstandighede word ondersoek deur simulasie, en twee aanpasbare beheer strategieë word ontwikkelom die oordrag te verbeter. Die aanpasbare beheer strategieë meng elemente van "bang-bang" beheer om die gehalte te verbeter, en gebande beheer tegnieke om die robuustheid van die stelsel te verbeter. Hierdie beheer strategieë is deeglik in simulasies getoets en die resultate is vergelyk met dié van die klassieke beheerder. Ekstensiewe modelleering van die stelsel is in die MATLAB™ omgewing gedoen om die beheerders te analiseer, en hardeware sensore is gebou om realistiese orientasie metings aan die beheerders te verskaf.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2015. / A precise orbit propagator was developed for implementing on a CubeSat's on-board computer for real-time orbital position and velocity determination and prediction. Knowledge of the accurate orbital position and velocity of a Low Earth Orbit (LEO) Cubesat is required for various applications such as antenna and imager pointing. Satellite motion is governed by a number of forces other than Earth's gravity alone. The inclusion of perturbation forces such as Earth's aspheric gravity, third body attraction (e.g. Moon and Sun), atmospheric drag and solar radiation pressure, is subsequently required to improve the accuracy of an orbit propagator. Precise orbit propagation is achieved by numerically integrating a set of coupled second order differential equations derived from satellite's perturbed equations of motion. For the purpose of this study two numerical integrators were selected: RK4 - Fourth order Runge Kutta method and RKF78 - results from embedding RK7 into RK8. The former is a single-step integrator while the latter is a multi-step integrator. These integrators were selected for their stability, high accuracy and computational efficiency. An orbit propagation software tool is presented in this study. Considering the processing power of Central Processing Unit (CPU) of CubeSat's on-board computer and a trade-off between precision and computational cost, the 10 x 10 and 20 x 20 gravity field models, the Exponential atmospheric model and Jacchia 70 static atmospheric model, were implemented. A 60 x 60 gravity field model is also investigated for reference. For validation purpose the developed software tool results were compared with results from Systems Tool Kit (STK) and Satellite Laser Ranging (SLR) using SUNSAT satellite reference orbit. / National Research Foundation

For the implementation of the NASA EOS testbed programmable operations, a control/data acquisition system has been designed, implemented, and tested. The work is focused mainly on the hardware design/build of the custom interface board and software development for real-time control and data acquisition of the testbed. Also, an application program was designed to control, collect, and display the data and parameters of the testbed elements, and troubleshoot the hardware. An algorithm was chosen and applied to the battery simulator control after computer simulations. The final experiment results were obtained successfully, which proved the design to be correct, as the testbed could be operated under computer control. / Master of Science

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Microfiche copy available in Archives and Barker. / Vita. / Includes bibliographical references. / by Roderick A. Hyde. / Ph.D.

Thesis (MScEng)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: The use of commercial-off-the-shelf components in low earth orbit (LEO) satellite systems has become a very popular design trend. Not only are many of these components sufficiently radiation tolerant, but are also less expensive than their space qualified counterparts. Commercial processors are already used in the on-board computer (OBC) of satellites like SUNSAT 2004, CanX and SNAP-I. With the increasing demand for smaller, less expensive satellites and a shorter time-to-market window, the feasibility of implementing a satellite's OBC as a system-on-a-chip (SoC) is now considered. This thesis describes a single-chip implementation, excluding memory, of a LEO microsatellite's OBC on the commercial grade Altera Excalibur embedded processor. A typical satellite OBC system was developed on the Excalibur device to test the functionality and performance of the device as a single-chip OBC. / AFRIKAANSE OPSOMMING: Die gebruik van kommersiële komponente in lae aardwentelbaan satelliet stelsels het 'n baie gewilde ontwerps neiging geword. Meeste van hierdie komersiële komponente is nie net voldoende bestand teen die radiasie in die ruimte nie, maar boonop goedkoper as soortgelyke komponente wat spesifiek vir de ruimte vervaardig is. Kommersiële verwerkers word alreeds gebruik in die aanboord rekenaar (AR) van satelliete soos SUNSAT 2004, CanX and SNAP-I. Met die aahoudende aanvraag vir kleiner, goedkoper en 'n korter ontwikkelings tydperk, word die implementering van 'n satelliet se AR as 'n stelsel-op-'nskyfie nou oorweeg. Hierdie tesis beskryf 'n enkel-skyfie implementasie, geheue uitgesluit, van 'n lae aardwentelbaan mikrosatelliet se AR op die kommersiële Altera Excalibur geïntregreerde verwerker. 'n Tipiese AR stelsel was ontwikkelop die Excalibur verwerker om die funksionaliteit en werkverrigting van die toestel as 'n enkel-skyfie AR te toets.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: After SUNSAT was launched in 1999 and the possibility of developing another micro satellite emerged, areas of possible improvement were identified. Among the suggestions that emerged was the idea of developing an on-board computer for a micro satellite, using one of the new generation low power processors. The processor had to meet guideline specifications derived from the experience gained by researchers and students involved with the SUNSAT project. This thesis covers the process of choosing one of these processors and the subsequent testing of the feasibility of using it in an on-board computer. The feasibility test included comparing the processor's specifications to those required and designing an evaluation board for this processor to test its ease of use and programmability. / AFRIKAANSE OPSOMMING: Nadat SUNSAT in 1999 gelanseer is en die moontlikheid vir die ontwikkeling van In soortgelyke satellite ontstaan het, is areas vir verbetering op bestaande stelsels geidentifiseer. Die idee om In nuwe generasie verwerker met lae kragverbruik as In aanboord rekenaar te gebruik, was een moontlikheid wat ondersoek moes word. Die verwerker moes aan riglyne gemeet, word wat afgelei is uit die ondervinding wat deur navorsers en studente tydens die SUNSAT projek opgedoen is. Die tesis dek die proses wat gevolg is om In verwerker te kies en die daaropvolgende toetsing om die bruikbaarheid van die verwerker as In aanboord rekenaar te bepaal. As deel van die toetsing is die verwerker se spesifikasies teen die verlangde spesifikasies opgeweeg, en In evaluasiebord is ontwikkel om die gemaklikheid van die gebruik en programmering van die verwerker te bepaal.